GB2363162A

GB2363162A - Solid state lift for micrometering in a fuel injector

Info

Publication number: GB2363162A
Application number: GB0108824A
Authority: GB
Inventors: David M Milam; Chien Chang Lee; Thomas S Carroll; Charles R Miller
Original assignee: Caterpillar Inc
Current assignee: Caterpillar Inc
Priority date: 2000-06-09
Filing date: 2001-04-09
Publication date: 2001-12-12
Anticipated expiration: 2021-04-09
Also published as: GB2363162B; GB0108824D0; DE10111504A1; US6363913B1

Abstract

A fuel injector performs main fuel injection by raising fuel pressure in a nozzle chamber (30) to lift a check valve member (26) to a fully open position, and performs preinjection or microinjection by operating a solid state motor (22) to lift the check valve member (26) a much smaller distance. The solid state motor (22) may be an expansion device, eg of piezoelectric or magnetostrictive material. The invention provides a reliable mechanism for accurately varying the check valve member (26) for rate shaping purposes.

Description

2363162

1 Description

2 3 SOLID STATE LIFT FOR MICROMETERING IN A FUEL INJECTOR 4 5 Technical Field

6 This invention relates generally to fuel 7 injectors utilizing check valves, and more 8 particularly to micrometering or varying fuel 9 injection rates using a solid state motor to lift a 10 check valve.

11 12 Background Art

13 Over time, engineers have come to recognize 14 that undesirable exhaust emissions can be reduced by 15 having the ability to produce at least three 16 different fuel injection rate shapes across the 17 operating range of a given engine. These rate shapes 18 include a ramp, a boot shape, and square fuel 19 injection profiles. In addition to these rate 20 shapes, there is often a need for the injector to 1 have the ability to produce split injections in order 2 to further improve combustion efficiency at some 3 operating conditions, such as at idl.e.

4 Although there exist a wide variety of 5 mechanisms for pressurizing fuel in fuel injection 6 systems, almost all fuel injectors include a spring 7 biased needle check valve to open and close the 8 nozzle outlet. In almost all fuel injectors, the 9 needle valve member is only stoppable at two 10 different positions: fully open or fully closed.

11 Because the needle valve members in these fuel 12 injectors are not normally stoppable at a partially 13 open position, fuel injection mass flow can usually 14 be controlled only through changes in fuel pressure.

15 Hydraulic bias control of the check valve 16 is also possible, such as taught in U.S. Patent No.

17 6,024,296 to Wear et al. Another approach is dual 18 nozzle design, but this is an expensive solution.

19 It would be advantageous to have a reliable 20 mechanism for accurately varying check lift for rate 21 shaping purposes. For example, reducing maximum lift 22 of the check valve member could provide pre-metering 23 or micrometering -- that is, injecting a very small 24 amount of fuel prior to a main injection -- or post 25 metering. This is highly desirable in order to 26 improve operation of the fuel injector, especially to 27 reduce noxious emissions and/or to reduce noise of 28 operation. Variable check lift could be advantageous 29 at other times as well. Accurate methods of 30 achieving very small fuel volume pre-metering or 31 micrometering are always of interest.

1 While it has been proposed in the art that 2 piezoelectric actuators could be employed in fuel 3 injection systems, the use of piezoelectric actuators 4 to directly control needle lift has proven somewhat 5 problematic. First, this is due in part to the fact 6 that only so much space is available within a fuel 7 injector to place a piezoelectric crystal stack.

8 Given the space limitations, the maximum 9 piezoelectric deformation possible in the space 10 available is generally on the order of less than 11 about one hundred microns. Since typical needle 12 valve lifts are on the order of several hundreds of 13 microns, direct piezoelectric control of needle valve 14 lift is not realistic without making substantial and likely unrealistic - changes in the nozzle area 16 of a fuel injector.

17 The present invention is directed to 18 addressing these and other concerns associated with 19 controlling needle valve lift within fuel injectors.

21 Disclosure of the Invention

22 In one aspect of the invention, a fuel 23 injector comprises a nozzle at least partially 24 defining a nozzle chamber and at least one injection 25 orifice. A check valve member extends into the 26 nozzle chamber and is slidably disposed in a nozzle 27 body between a first position in which the check 28 valve member obstructs fluid communication between 29 the nozzle chamber and the injection orifice and a 30 second position in which the nozzle chamber and the 31 injection orifice are in fluid communication. A 1 solid state motor in the nozzle body is capable of 2 moving the check valve member toward the second 3 position.

4 In another aspect of the invention, a 5 method is given for operating a fuel injector having 6 a check valve member slidably disposed in a nozzle 7 body and movable through a range of motion. The 8 range of motion includes a first position in which 9 the check valve member obstructs fluid communication 10 between a nozzle chamber in the nozzle body and at 11 least one orifice in the nozzle body, a second 12 position in which the nozzle chamber and the orifice 13 are in fluid communication, and a third position 14 between the first position and the second position, 15 and substantially closer to the first position than 16 to the second position, in which the check valve 17 member substantially but not entirely restricts fluid 18 communication between the nozzle chamber and the 19 orifice. The method comprises a fuel pressurization 20 step of increasing fuel pressure in the nozzle 21 chamber, a micrometering injection step of operating 22 a solid state motor in the nozzle body to slide the 23 check valve member from the first position to stop at 24 the third position, and a main injection step of 25 increasing fuel pressure in the nozzle chamber to a 26 pressure level sufficient to slide the check valve 27 member in the nozzle body to the second position.

28 29 Brief Description of the Drawings

30 Features of the invention can be better 31 understood with reference to the drawing figures, in 1 which certain dimensions may be exaggerated to 2 illustrate check valve movement for example, and in 3 which:

4 FIG. 1 is a diagrammatic side view 5 representation of a fuel injector utilizing a solid 6 state lift according to the invention; 7 FIG. 2 is a diagrammatic side view 8 representation of a check valve portion of the fuel 9 injector of FIG. 1 with the check in a first 10 position; 11 FIG. 3 is a diagrammatic side view 12 representation of the check valve portion of FIG. 2 13 with the check in a second position; 14 FIG. 4a is a diagrammatic side view is representation of the check valve portion of FIG. 2 16 with the check in a third position; and 17 FIG. 4b is a diagrammatic side view 18 representation of an alternate embodiment of a check 19 piston that can be used with the invention.

21 Best Mode for Carrying Out the Invention

22 The invention is now described with 23 reference to FIGS. 1-4b, which illustrate a fuel 24 injector 10 and check valve portion 12 thereof 25 utilizing the invention.

26 The fuel injector 10 in this embodiment, 27 shown in FIG. 1, is a hydraulically actuated fuel 28 injector and has an electronically controlled 29 actuator 14. In the illustrated embodiment the 30 actuator 14 utilizes a solenoid, but other types of 31 electronically controlled actuators, for example 1 piezo or magnetostrictive, may be used. In other 2 embodiments mechanical actuators may be used.

3 An intensifier piston 16 is slidably 4 disposed in the fuel injector 10. Beneath the 5 intensifier piston 16 is a plunger 18 partially 6 defining a fuel pressure control cavity 20. In other 7 embodiments the plunger 18 may be integral with the 8 intensifier piston 16.

9 FIGS. 2-4b show a check valve portion 12 of 10 the fuel injector 10 in greater detail. A solid 11 state motor 22 is disposed in a nozzle body 24 12 against a check valve member 26. The solid state 13 motor 22 can be an expansion device composed of any 14 electrically or magnetically expandable material, is piezo or magnetostrictive for example. The device or 16 the material from which it is made may expand when 17 energized, as with a standard piezo stack for 18 example, or may contract when energized, for example 19 when using a thermally pre-stressed, bending unimorph 20 piezo device comprising ferroelectric wafers such as 21 those described in U.S. Patent No. 5,632,841 assigned 22 to the National Aeronautics and Space Administration 23 (NASA).

24 The check valve member 26 -is slidably 25 disposed in a check bore 28 in the nozzle body 24, 26 and extends into a nozzle chamber 30 in a nozzle 32.

27 The nozzle 32 has at least one injection orifice 34.

28 Above the check valve member 26 is a check piston 36 29 that can be a separate piece from the check valve 30 member 26 as in the illustrated embodiment, or can be 1 attached to, or can even be part of, the check valve 2 member 26.

3 In the embodiment illustrated in FIGS. 1-4a 4 the check piston 36 incorporates a glide ring seal 38 5 comprising a rubber energizer or O-ring 40 and a 6 nylon wear surface 42. The check piston 36 with the 7 glide ring seal 38 is slidably disposed in a check 8 piston bore 44. FIG. 4b shows an alternate 9 embodiment of a check piston 361 without the glide 10 ring seal 38.

11 A check control chamber 46 is partially 12 defined by a closing hydraulic surface 48 of the 13 check piston 36. In the illustrated embodiment a 14 mechanical bias 50 such as a spring for example in is the check control chamber 46 pushes downward on the 16 check piston 36. A check stop 52 also extends into 17 the check control chamber 46 in the illustrated 18 embodiment.

19 20 Industrial Applicability

21 The fuel injector 10 in the illustrated 22 embodiment of FIGS. 1 and 2 is a hydraulically 23 actuated fuel injector with direct check control 24 utilizing the invention.' of course, it will be 25 understood that the invention can also be practiced 26 in a hydraulically actuated fuel injector without 27 direct check control, as well as in a non 28 hydraulically (i.e., mechanically) actuated fuel 29 injector with or without direct check control.

30 Fuel injection occurs when the check valve 31 member 26 is pulled or pushed upward so that high 1 pressure fuel in the nozzle chamber 30 can pass 2 through the injection orifice 34. Usually there will 3 be more than one injection orifice 34 arranged for 4 efficient fuel injection.

5 The check valve member 26 is usually biased 6 downward to keep it from opening, that is, to keep 7 the check valve member 26 in a first position, i.e., 8 a "closed" position, shown in FIG. 2, in which it is 9 pressed against the nozzle 32 to fluidly isolate the 10 injection orifice 34 from the nozzle chamber 30.

11 This bias may be mechanical or hydraulic.

12 The illustrated embodiment uses both 13 mechanical and hydraulic bias to keep the check valve 14 member 26 biased toward the first position. The is mechanical bias 530 presses downward on the check 16 piston 36. Additionally, high-pressure hydraulic 17 fluid can be diverted to the check control chamber 46 18 to apply additional downward bias against the check 19 piston 36.

20 Main fuel injection occurs when fuel 21 pressure in the nozzle chamber 30 is increased until 22 the fuel pressure in the nozzle chamber 30 overcomes 23 the mechanical and/or hydraulic bias keeping the 24 check valve member 26 in the first position. When 25 this happens the check valve member 26 slides upward 26 to a second position, i.e., an "open" position, shown 27 in FIG. 3. In the illustrated embodiment upward 28 movement of the check valve member 26 is terminated 29 by contact with the check stop 52. other embodiments 30 could dispense with the check stop 52, relying on 1 mechanical and/or hydraulic bias to halt upward 2 movement of the check valve member 26.

3 In the illustrated embodiment fuel pressure 4 in the nozzle chamber 30 is increased for main fuel 5 injection by causing the actuator 14 to direct high 6 pressure actuation fluid to push against the 7 intensifier piston 16. This in turn pushes the 8 plunger 18 further into the fuel pressure control 9 cavity 20, which raises fuel pressure in both the 10 fuel pressure control cavity 20 and in the nozzle 11 chamber 30 to which it is fluidly connected.

12 Main fuel injection ends when the total 13 bias pushing the check valve member 26 toward the 14 first position exceeds the fuel pressure in the 15 nozzle chamber 30. This can be accomplished by 16 reducing fuel pressure in the nozzle chamber 30, by 17 increasing downward bias against the check valve 18 member 26, or by a combination of those two methods.

19 In the illustrated embodiment fuel pressure 20 in the nozzle chamber 30 can be reduced by operating 21 the actuator 14 to release hydraulic fluid pressure 22 from pushing on the intensifier piston 16, thereby 23 allowing the plunger 18 to move upward again. of 24 course, in other fuel injector embodiments other 25 methods of increasing and decreasing fuel pressure in 26 the nozzle chamber 30 may be used with the invention.

27 In the illustrated embodiment the downward 28 bias against the check valve member 26 can be - 29 increased to end main fuel injection by operating the 30 actuator 14 to direct high-pressure actuation fluid 31 into the check control chamber 46. Of course, in 1 other fuel injector embodiments other methods of 2 increasing downward bias against the check valve 3 member 26 to end main fuel injection may be used with 4 the invention. In some embodiments a constant 5 mechanical or other bias may be used. In other 6 embodiments utilizing the invention a hydraulic bias, 7 either constant or variable, may be used in place of 8 the mechanical bias 50. Still other embodiments may 9 use combinations of these methods for providing bias 10 when utilizing the invention.

11 Micrometering injection occurs when the 12 solid state motor 22 is changed from a first energy 13 state in which t'he check valve member 26 can slide to 14 or remain at the first position, to a second energy 15 state in which the solid state motor 22 pulls or 16 pushes the check valve member 26 upward to a third 17 position, i.e., a I'micrometering" position, shown in 18 FIG. 4a. This movement is generally very small 19 compared with the movement of the check valve 20 member 26 from the first position to the second 21 position, so tha in the third position the check 22 valve member 26 still substantially but not entirely 23 restricts fuel in the nozzle chamber 30 from reaching 24 the injection orifice 34. This allows a small amount 25 of highly pressurized fuel to be ejected for pre 26 metering or micrometering, but much less than would 27 be expected for the main injection.

28 Micrometering injection ends either when 29 main fuel injection begins, or when the solid state 30 motor 22 is changed from the second energy state back 31 to the first energy state, allowing the downward bias 1 on the check valve member 26 to push the check valve 2 member 26 back to the first position.

3 Any number of fuel injection sequence 4 combinations can be imagined. For example, before 5 fuel pressure in the nozzle chamber 30 is high enough 6 to push open the check valve member 26 to the second 7 position against the bias of the check spring, the 8 solid state motor 22 can move the check valve 9 member 26 to the third position for pre-metering.

10 Then, fuel pressure in the nozzle chamber 30 can be 11 raised to move the check valve member 26 from the 12 third position to the second position for main fuel 13 injection. Or, the solid state motor 22 can release 14 the check valve member 26 allowing it to return to 15 the first (closed) position before fuel pressure in 16 the nozzle chamber 30 is high enough to offset the 17 bias downward against the check valve member 26, to 18 cause a pause in micrometering before main injection 19 begins.

20 Or, in the case of a fuel injector with 21 direct check control, the solid state motor 22 can be 22 operated to raise the check valve member 26 from the 23 first (closed) position to the third (micrometering) 24 position even while actuation fluid pressure in the 25 check control chamber 46 is high enough to prevent 26 the check valve member 26 from being opened in 27 response to high fuel pressure in the nozzle 28 chamber 30. Any number of such combinations can be 29 easily imagined.

30 Additionally, the solid state motor 22 can 31 move the check valve member 26 to a fourth position 1 different from the third position, or to any of a 2 plurality of different positions, by varying the 3 current or magnetic field applied to the solid state

4 motor 22 (piezo or magnetostrictive type, for 5 example). In this way the amount of fuel injected 6 during micrometering injection can be varied. In 7 this way the solid state motor 22 can move the check 8 valve member 26 from the first position to any of the 9 plurality of positions, or from one of the plurality 10 of positions to another.

11 In the illustrated embodiment, the glide 12 ring seal 38 of the check piston 36 fluidly isolates 13 hydraulic fluid in the check control chamber 46 from 14 any fuel that may have seeped through the check 15 bore 28 from the nozzle chamber 30. The nylon wear 16 surface 42 of the glide seal ring 38 provides good 17 wear characteristics but has little or no elasticity, 18 so the rubber energizer 40 pushes it against the 19 check piston bore 44.

20 In embodiments using a fuel injector 21 without direct hydraulic check control there may be 22 no need for high-pressure hydraulic actuation fluid 23 in the check control chamber 46, and thus the check 24 piston 36 with the glide ring seal 38 may not be 25 necessary. In that case the check piston 36 could be 26 merely a top portion of the check valve member 26.

27 While the invention has been illustrated 28 and described in detail in the drawings and foregoing 29 description, such illustration and description are to

30 be considered illustrative or exemplary and not 31 restrictive; the invention is not limited to the 1 disclosed embodiments. Other variations to the 2 disclosed embodiments can be understood and effected 3 by those skilled in the art in practicing the claimed 4 invention, from a study of the drawings, the 5 disclosure, and the appended claims.

Claims

1. A fuel injector comprising:

a nozzle at least partially defining a 5 nozzle chamber and at least one injection orifice; a check valve member extending into the nozzle chamber and slidably disposed in a nozzle body between a first position in which the check valve member obstructs fluid communication between the 10 nozzle chamber and the injection orifice and a second position in which the nozzle chamber and the injection orifice are in fluid communication; and a solid state motor in the nozzle body capable of moving the check valve member toward said 15 second position.

2. The fuel injector of claim 1, further comprising a mechanical bias biasing the check valve member toward said first position.

3. The fuel injector of either claim 1 or claim 2, further comprising a check control chamber fluidly isolated from the nozzle chamber and fillable with high-pressure hydraulic fluid such that fluid 25 pressure of the high-pressure hydraulic fluid in the check control chamber will bias the check valve member toward said first position.

4. The fuel injector of claim 3, further 30 comprising glide ring seal means for fluidly isolating the check control chamber from the nozzle chamber.

5. The fuel injector of any preceding 5 claim, wherein said solid state motor is a piezo device.

6. The fuel injector of any of claims 1 to 4, wherein said solid state motor is a 10 magnetostrictive device.

7. The fuel injector of any preceding claim, further comprising:

an intensifier piston slidably disposed in is the fuel injector and operable to increase fuel pressure in the nozzle chamber; and an actuator operable to divert high pressure actuation fluid to the intensifier piston.

20

8. A method for operating a fuel injector having a check valve member slidably disposed in a nozzle body and movable through a range of motion, the range of motion including:

a first position in which the check valve 25 member obstructs fluid communication between a nozzle chamber in the nozzle body and at least one orifice in the nozzle body; a second position in which the nozzle chamber and the orifice are in fluid communication; 30 and a third position between the first position and the second position, and substantially closer to the first position than to the second position, in which the check valve member substantially but not 5 entirely restricts fluid communication between the nozzle chamber and the orifice, the met-hod comprising:

a fuel pressurization step of increasing fuel pressure in the nozzle chamber; 10 a micrometering injection step of operating a solid state motor in the nozzle body to slide the check valve member from the first position to stop at the third position; and a main injection step of increasing fuel 15 pressure in the nozzle chamber to a pressure level sufficient to side the check valve member in the nozzle body to the second position.

9. The method of claim 8, further 20 comprising operating the solid state motor to slide the check valve member to stop at a fourth position different from the third position.

10. The method of claim 8, further 25 comprising performing the main inject-ion step when the micrometering injection step has been performed and the check valve member is at the third position.

11. The method of claim 8, further comprising:

operating the solid state motor to slide the check valve member from the third position to the first position; and performing the main injection step when the 5 check valve member is at the first position.

12. The method of claim 8, further comprising performing the micrometering injection step when the check valve member is at an 10 intermediate position between the first position and the second position.

13. The method of any of claims 8 to 12, further comprising using a mechanical bias to bias 15 the check valve member toward the first position.

14. The method of any of claims 8 to 13, further comprising diverting high-pressure hydraulic fluid to a check control chamber fluidly isolated 20 from the nozzle chamber to bias the check valve member toward the first position.

15. The method of any of claims 8 to 14, wherein the fuel pressurization step comprises using 25 high-pressure hydraulic fluid to drive a plunger to increase fuel pressure in a fuel pressure control cavity by decreasing the volume of the fuel pressure control cavity.

30

16. The method of claim 15, further comprising electronically operating an actuator to divert high-pressure actuating fluid to an intensifier piston to drive the plunger.

17. The method of claim 16, further 5 comprising causing the check valve member to slide from the second position to one of the first position and the third position by diverting high-pressure hydraulic fluid to a check control chamber fluidly isolated from the nozzle chamber.

18. The method of any of claims 8 to 17, wherein the solid state motor is a magnetostrictive device.

15

19. The method of any of claims 8 to 17, wherein the solid state motor is a piezo device.

20. The method of claim 19, wherein the micrometering injection step is performed by 20 deenergizing the piezo device.

21. A fuel injector substantially as hereinbefore described with reference to the accompanying drawings. 25

22. A method for operating a fuel injector substantially as hereinbefore described with reference to the accompanying drawings.